Conventionally, two types of devices, namely thermionic and cold cathode devices, are known as electron-emitting devices. Known examples of the cold cathode devices are field emission type electron-emitting devices (to be referred to as FE type electron-emitting devices hereinafter), and metal/insulator/metal type electron-emitting devices (to be referred to as MIM type electron-emitting devices hereinafter). A known example of surface-conduction emission type electron-emitting devices is described in, e.g., M. I. Elinson, “Radio Eng. Electron Phys., 10, 1290 (1965) and other examples will be described later.
The surface-conduction emission type electron-emitting device utilizes the phenomenon that electrons are emitted by a small-area thin film formed on a substrate by flowing a current in parallel with the film surface. The surface-conduction emission type electron-emitting device includes electron-emitting devices using an Au thin film [G. Dittmer, “Thin Solid Films”, 9,317 (1972)], an In2O3/SnO2 thin film[M. Hartwell and C. G. Fonstad, “IEEE Trans. ED Conf.”, 519 (1975)], a carbon thin film[ Hisashi Araki et al., “Vacuum”, Vol. 26, No. 1, p. 22 (1983)], and the like, in addition to an SnO2 thin film according to Elinson mentioned above.
Known examples of the FE type electron-emitting devices are described in W. P. Dyke and W. W. Dolan, “Field emission”, Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, “Physical properties of thin-film field remission cathodes with molybdenium cones”, J. Appl. Phys., 47, 5248 (1976).
As another FE type device structure, there is an example in which an emitter and gate electrode are arranged on a substrate to be almost parallel to the surface of the substrate.
A known example of the MIM type electron-emitting devices is described in C. A. Mead, “Operation of tunnel emission Devices”, J. Appl. Phys., 32,646 (1961).
Since the above-described cold cathode devices can emit electrons at a temperature lower than that for thermionic cathode devices, they do not require any heater. The cold cathode device has a structure simpler than that of the thermionic cathode device and can shrink in feature size. Even if a large number of devices are arranged on a substrate at a high density, problems such as heat fusion of the substrate hardly arise. In addition, the response speed of the cold cathode device is high, while the response speed of the thermionic cathode device is low because thermionic cathode device operates upon heating by a heater.
For this reason, applications of the cold cathode devices have enthusiastically been studied.
Of cold cathode devices, the surface-conduction emission type electron-emitting devices have a simple structure and can be easily manufactured, so that many devices can be formed on a wide area. As disclosed in Japanese Patent Laid-Open No. 64-31332 filed by the present applicant, a method of arranging and driving many devices has been studied.
Regarding applications of the surface-conduction emission type electron-emitting devices, e.g., image forming apparatuses such as an image display apparatus and image recording apparatus, charge beam sources, and the like have been studied.
Particularly as an application to image display apparatuses, as disclosed in the U.S. Pat. No. 5,066,883 and Japanese Patent Laid-Open Nos. 2-257551 and 4-28137 filed by the present applicant, an image display apparatus using a combination of a surface-conduction emission type electron-emitting device and a fluorescent substance which emits light upon irradiation with an electron beam has been studied. This type of image display apparatus using a combination of the surface-conduction emission type electron-emitting device and fluorescent substance is expected to exhibit more excellent characteristics than other conventional image display apparatuses. For example, compared to recent popular liquid crystal display apparatuses, the above display apparatus is superior in that it does not require any backlight because of self-emission type and that it has a wide view angle.
A method of driving a plurality of FE type electron-emitting devices arranged side by side is disclosed in, e.g., U.S. Pat. No. 4,904,895 filed by the present applicant. A known application of FE type electron-emitting devices to an image display apparatus is a flat panel display apparatus reported by R. Meyer et al. [R. Meyer: “Recent Development on Microtips Display at LETI”, Tech. Digest of 4th Int. Vacuum Microelectronics Conf., Nagahara, pp. 6-9 (1991)]. An application of many MIM type electron-emitting devices arranged side by side to an image display apparatus is disclosed in Japanese Patent Laid-Open No. 3-55738 filed by the present applicant.
FIG. 1 shows an example of a multi electron source wiring method. In the electron source shown in FIG. 1, m cold cathode devices in the vertical direction and n cold cathode devices in the horizontal direction, i.e., a total of n×m cold cathode devices are two-dimensionally arrayed in a matrix. In FIG. 1, reference numeral 3074 denotes a cold cathode device; 3072, a row-direction wiring line; 3073, a column-direction wiring line; 3075, a wiring resistance of the row-direction wiring line; and 3076, a wiring resistance of the column-direction wiring line. Reference symbols Dx1, Dx2, . . . , Dxm denote feeding terminals of the row-direction wiring lines; and Dy1, Dy2, . . . , Dyn, feeding terminals of the column-direction wiring lines. This simple wiring method is called a matrix wiring method. The matrix wiring method can easily manufacture a multi electron source because of a simple structure.
When a multi electron beam by the matrix wiring method is to be applied to an image forming apparatus, m and n must be several hundreds or more in order to ensure the display capacitance. Further, a cold cathode device must accurately output an electron beam with a desired intensity in order to display an image at an accurate luminance.
When many cold cathode devices wired in a matrix are to be driven, devices of one row of the matrix are simultaneously driven. The row to be driven is sequentially switched to scan all the rows. According to this method, the driving time assigned each device is ensured n times longer than in a method of sequentially scanning all the devices one by one. Thus, the luminance of the display apparatus can be increased.
More specifically, there are proposed an arrangement in which a voltage source is connected to matrix wiring to drive devices, and a method of driving FE type devices using a controlled constant current source, as disclosed in U.S. Pat. No. 5,300,862 to Parker et al. FIG. 2 is a circuit diagram for explaining this.
In U.S. Pat. No. 5,300,862, the X direction shown in FIG. 2 is a row direction, and the Y direction is a column direction. In the following description, however, the X direction is defined as a column direction, and the Y direction is defined as a row direction in order to match the description of the present invention.
In FIG. 2, reference numerals 2201a, 2201b, and 2201c denote controlled constant current sources; 2202, a switching circuit; 2203, a voltage source; 2204a, column wiring lines; 2204b, row wiring lines; and 2205, FE type devices.
The switching circuit 2202 selects one of the row wiring lines 2204b, and connects it to the voltage source 2203. The controlled constant current sources 2201a, 2201b, and 2201c supply currents to the respective column wiring lines 2204a. These operations are properly performed in synchronism with each other to drive FE type devices of one row.
Arrangements in which an electron source having surface-conduction emission type electron-emitting devices is driven using a constant current source are disclosed in European Patent Laid-Open EP688035A, EP762371A, EP762372A, and EP798691A.